[Docs] Improve API documentation for authentication and API key management

[Gautam25Raj]

Summary

This PR updates and improves API documentation to better reflect existing authentication and API key management features.

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Docs

Authentication Documentation

• Documented API key authentication flow
• Added email OTP authentication endpoints:
  • Send OTP
  • Verify OTP

API Key Documentation

• Added detailed documentation for API key endpoints:
  • List, create, rotate, revoke, and delete
• Improved response schemas and examples

OpenAPI Improvements

• Updated OpenAPI spec with clearer structure and definitions
• Added proper error responses (bad request, not found, etc.)
• Organized API paths into separate files for better maintainability

Notes

• No code changes
• Documentation-only update
• Improves clarity and developer experience for API usage

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📝 Documentation update
• 🧪 Tests (adding or updating tests)

Checklist

• [x I have read the CONTRIBUTING.md document.
• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• Any dependent changes have been merged and published in downstream modules.